Relevance of the correlation between precipitation and the 0 °C isothermal altitude for extreme flood estimation

Abstract

a b s t r a c tExtreme floods are commonly estimated with the help of design storms and hydrological models. In this paper, we propose a new method to take into account the relationship between precipitation intensity (P) and air temperature (T) to account for potential snow accumulation and melt processes during the elaboration of design storms. The proposed method is based on a detailed analysis of this P-T relationship in the Swiss Alps. The region, no upper precipitation intensity limit is detectable for increasing temperature. However, a relationship between the highest measured temperature before a precipitation event and the duration of the subsequent event could be identified. An explanation for this relationship is proposed here based on the temperature gradient measured before the precipitation events. The relevance of these results is discussed for an example of Probable Maximum Precipitation-Probable Maximum Flood (PMP-PMF) estimation for the high mountainous Mattmark dam catchment in the Swiss Alps.The proposed method to associate a critical air temperature to a PMP is easily transposable to similar alpine settings where meteorological soundings as well as ground temperature and precipitation measurements are available. In the future, the analyses presented here might be further refined by distinguishing between precipitation event types (frontal versus orographic).

Swiss Rainfall Mass Curves and their Influence on Extreme Flood Simulation

“…The model was duly calibrated and validated against observed data (for details see Zeimetz 2017;Zeimetz et al in press). The hydrological model was initialized with the same values for all seasons (no snow, 30% of soil saturation) and with a 0_C isothermal altitude at 4500 m asl., which ensures absence of snowfall on the entire catchment (Zeimetz et al 2017). This ensures that the results are independent of air temperature and initial catchment conditions.…”

Why do we have so many different hydrological models? A review based on the case of Switzerland

“…Any model‐based flood estimation method is computationally intensive since long model simulation runs are required at an hourly time step (see Sikorska‐Senoner et al, 2020, about reducing computational requirements for extreme flood estimation by hydrological modeling). Accordingly, simple models such as PREVAH (Felder & Weingartner, 2017; Viviroli, Mittelbach, Gurtz, & Weingartner, 2009; Viviroli, Zappa, Schwanbeck, et al, 2009), HBV‐light (Brunner & Sikorska‐Senoner, 2019; Sikorska et al, 2017; Sikorska‐Senoner et al, 2020) and RS MINERVE (Bieri & Schleiss, 2013; Zeimetz et al, 2017, 2018) are often used for flood estimation; these models are all deemed to perform well enough for flood estimation in Swiss catchments by their respective authors and users. Furthermore, at the time of writing, the open‐source DECIPHeR model is further developed and implemented for Swiss catchments to bring diversity in the type of models used for flood modeling (Kauzlaric, personal communication).…”

New Approach to Identifying Critical Initial Conditions for Extreme Flood Simulations in a Semicontinuous Simulation Framework

“…The height of the 0°C isothermal altitude has been fixed at H ¼ 4,780 m ASL, according to the maximum observed isothermal altitude before a 3-h rainfall event in the southern part of the Alps (Zeimetz et al 2017). The temperature conditions are thus high enough to avoid snowfall during the PMP event.…”